Polypeptides and other compounds that can bind specifically to the CH2-CH3 cleft of an immunoglobulin molecule, as well as methods for using such polypeptides and compounds to inhibit Fc-mediated immune complex formation in viral infection, are described. For example, polypeptides and other compounds can be used to inhibit binding of DF-associated, immune-complexed IgG anti-DF viron(s) or DV viral antigens to F&gammaR, ADE of DF/DHF/DSS infections by inhibition of DF viral antigen binding to immune complexed IgG, F&gammaR and immune complexed IgG mC1q (membrane C1q) or soluble C1q binding.
